Not Again
by Sheogorath's Avatar
Summary: After Halo 5: Guardians, Fireteam Osiris and Blue Team are pulled into the Ethereal war. XCOM may now start breathing a little easier, because Humanity's best soldiers are here. Rated M for gore and profanity. HDD ISSUES; Temporarily on hold.
1. Chapter 1

**A/N: I'm putting my other stories on hold until I can figure out where to go with them. I may even rewrite some of the worst bits. In the meantime, here is something I have been bouncing about my brainpan for a while.**

 **Genesis, 2558**

Cortana's guardian was escaping, Blue Team was sealed in a Cryptum, and Fireteam Osiris was on their last legs. In short, it was SNAFU. 031 Exuberant Witness, however, was relieved. "Cortana is now out of the systems, and I have regained full control of my installation! Thank you, reclaimers."

"Well, I'm glad that _someone_ is happy," Buck snapped.

"Cut the chatter, Osiris! We need to get Blue Team out of the cryptum," Locke interjected.

"Oh, that will be no problem. With my access restored, I can open the Cryptum, and release the other Reclaimers," replied Exuberant, happy to help. "Stand back!" With that, the cheerful monitor floated over to the sphere. A blue beam of light extended from it to the Cryptum. "Just a few more seconds." Finally, the device began to crack open. Osiris could now see the imposing silhouettes of the legendary soldiers. With a light hum, the Cryptum disappeared, dropping the SPARTANs to the floor with a loud thud. They picked themselves up, shaking of the Cryptum's effects. Their recovery was soon interrupted by an uncharacteristically worried Exuberant. "Reclaimers, I seem to have triggered a security system put in place by Cortana. We should most likely leave the area." Before the two teams of SPARTANs could comply, however, a swirling portal engulfed them before disappearing. "Oh, well. I suppose I should check the systems for any other similar devices. Wouldn't want that to happen to the next Reclaimers to arrive."

00000000

 **The Crystal Labyrinth, outside of time**

Somewhere, a Chaos God smiled. He reached out into the Immaterium, or Slipspace, or whatever the mortals called it, and plucked the travelers from it. ' _This should be entertaining_ ,' he thought as he shoved them onto another course. ' _They will disrupt so many delicate plans_.' He rubbed his gnarled hands together with glee. Yes, Tzeentch would enjoy watching this.

00000000

 **Hong Kong, 2015**

A pair of sectoids poked at a gel-covered body, preparing it for transport. Out of the corner of its eye, one of them noticed a flash of blue. It looked curiously in the direction of the flash, but didn't see anything of interest. It gave its race's equivalent of a shrug, and went back to the body. Any thoughts as to what it might have been exited the sectoid's mind, along with several chunks of grey matter as a 7.62mm bullet tore through its skull, reducing the head to pulp. Its partner's head shot up at the noise, but it suffered the same gory fate as Frederick-104 squeezed the trigger of his DMR a second time. Walking up to the corpses, both teams paused. "What the hell were those things?" Vale was the first to speak up.

Locke was quick to respond, "It don't know, but it appears to be responsible for this," he said while gesturing to the unfortunate abductee. "For now, treat all non-human contacts as hostile until we figure out where we are." In response, his team's icons flashed green on his HUD. "Let's keep moving."

"Fuck, fuck, fuck!" Operative Velasquez shouted as he fired an LMG burst into a nearby Thin Man. "Big Sky, this is Strike One-Actual. We need immediate evac NOW! Mills, Osterman, and Ryan are KIA, and I'm not sure how long Zhang can hold on!" Said soldier had taken a plasma bolt to the stomach, and was currently unconscious and mumbling something about a stolen diamond shipment. Mills, their Medic had been the first to die, a lucky plasma shot hitting the gas tank of the car he had been taking cover behind. Osterman, their Assault, had gotten too close to a Thin Man and choked to death on the poison. Ryan had been on a nearby rooftop, when a Floater shot the sniper in her back. The entire mission was FUBAR, and Velasquez was low on ammo. He heard the roar of an approaching Floater. He swung around to bring his gun to bear, only to hear the dreaded click of an empty magazine. "Shit!" he swore as he grabbed a frag grenade and prepared to go out with a bang. Before he could pull the pin, he heard a loud crack, and the alien was blown nearly in half. His head snapped towards the source of the noise, and he dropped the grenade in surprise and awe. Striding towards him were eight of the largest soldiers he had ever seen. The four in front must have been nearly seven feet tall, and were wearing angular, thick-looking plates of armor. The rear four were significantly shorter, only around 6', and their armor looked sleeker and lighter. Despite that, they looked just as lethal as the giants.

Their apparent leader, a titan in battle-scarred olive green spoke with a deep monotone, "Soldier, sitrep."

"Uhhh, Operative Velasquez, XCOM heavy. The one on the ground is Operative Zhang, also a heavy."

"XCOM?"

"The eXtraterrestrial COMbat unit, formed to defend Earth from the alien threat."

"We're on Earth?" the giant said with a tone of disbelief. Behind... Him?... It?, the others shifted and shot each other looks.

One of the smaller soldiers spoke up, "Well, ain't this just great. And I thought I'd had enough of alien invaders for a lifetime."

 **00000000**

 **So, here is the first chapter of my XCOM:EW/Halo crossover. I'm sorry if you were looking forward to another chapter of one of my other stories, so I promise that I will work on them as soon as I can. Also, while I did include a bit of WH40k, that was just to explain how our heroes traveled. I am not planning on adding any more, as the Ruinous Powers already have a galaxy of their own to mess with. Tzeentch is just doing this for a bit of fun.**


	2. Chapter 2

**A/N: I am surprised that people seem to like this story. Thank you to everyone who left a review or followed! This story will mostly focus on the interactions between the cast during the inter-mission downtime. Most missions will be skipped over, except for the big ones (Annette Durand, Slingshot, Temple Ship, or Site Recon.)**

 **Review responses:**

 **Guest-Thanks!**

 **phantomwa1ker- The Crystal Labyrinth and Tzeentch are from WH40K. As above, thanks for the review.**

 **Disclaimer: I own nothing and make no money.**

 **Military Jargon Dictionary:**

 **SNAFU- Situation Normal, All Fucked Up**

 **FUBAR- Fucked Up Beyond All Recovery.**

00000000

Velasquez couldn't believe his eyes. The eight strange soldiers were cutting through the aliens that had nearly wiped out his squad. The smaller soldier in the white armor was carrying Zhang in a fireman's carry and dashed from cover to cover with an abnormal speed. The larger ones moved about the battlefield with an almost mechanical precision, almost as if they had been doing this their entire lives. Out of the corner of his eye, he saw a flash of green. "Look out!" he shouted at one of the green-armored behemoths. The figure turned, but was struck by the plasma bolt. Velasquez flinched, expecting to see one of his mysterious saviors killed. He was shocked, then, to see the soldier still standing, with what appeared to be golden lightning flickering around the strange armor. He then heard a loud double crack, and the offending thin man disintegrated above the waist. The strangers' armaments were an order of magnitude more powerful than what the Argentinian had ever seen before. After that, the group reached the extraction point with no further incidents. Needless to say, BIG SKY was hesitant to let the new arrivals on board, but relented when Velasquez explained the situation. They quickly boarded the skyranger, and the white-armored one lifted up its helmet, revealing the face of a woman with short-cropped black hair.

"Locke, he's losing a lot of blood!" she shouted to her grey-armored comrade.

"Give him some biofoam. That should stabilize him for now." he replied in a commanding voice. The soldier in the lighter grey armor handed the woman a small canister. She shook it and pointed it at Zhang's wound.

"Hold on soldier, this is going to hurt." she said as she sprayed a thick substange from the can. Zhang grunted in pain but was otherwise silent. Zhang looked up, seemingly jolted out of his delirium.

"Thank you. Now, may I at least know who you guys are?" Velasquez asked. The dark grey soldier removed his helmet, revealing dark skin that was drenched in sweat.

"Jameson Locke, SPARTAN fireteam OSIRIS." The white-armored woman looked up.

"Holly Tanaka, also OSIRIS." The one who had handed Tanaka the canister also spoke up.

"Eddie Buck, and I'm with those two." he said gesturing to Locke and Tanaka. The one in red removed her helmet and said.

"Olympia Vale, the same." The four green-armored giants shared a look. One of them, who had the image of a rabbit carved onto her lapel spoke up first.

"SPARTAN Kelly-087, Blue Team." She nudged the soldier next to her, who towered over even the other giant soldiers. He grunted before replying.

"Fred-104, Blue Team." The one cradling a monster of a rifle looked up before speaking.

"Linda-058, Blue Team." The final one, who had been silent since his questioning of Velasquez spoke slowly but confidently.

"Master Chief Petty Officer Sierra-117, Blue Team." Velasquez took notice of the glances the rest of Blue Team shot 117, seemingly worried about him. Buck then spoke, cutting through the awkward silence.

"Well, now that we've said are part, ya mind filling us in as to what the hell is going on. Those guys didn't look like any covies I've ever seen."

Velasquez blinked in confusion at the term, but replied, "The little greys are called sectoids, they are weak, but they can be pretty dangerous in numbers. The skinny _pendejos_ are Thin Men, they are crack shots and can drop poison gas. The monstrosities are Floaters, they can be a bitch to outflank." Before the conversation could continue, BIG SKY announced that they were approaching XCOM HQ.

00000000

Central Officer Bradford was nursing a migraine, and the news from BIG SKY wasn't helping. More than half of Strike One were KIA, and one of them was seriously wounded. On top of that, there were the strangers that had showed up and saved the day. As he walked towards the Commander's office, he passed a group of orderlies wheeling Zhang to Medical. He noticed that a rather nasty plasma burn had been covered in some sort of tacky white foam. He sighed, the report would be an absolute bitch to write.


	3. Chapter 3

**A/N: Nothing much to report, so here is a random history fact: Conan's 'what is best in life' line from the 1989 movie is paraphrased from something said by Genghis Khan.**

 **Denalian & Phantomwa1ker: The main thing that I will be using from LW will be the larger squads. OSIRIS and Blue Team will mostly be on their own, as four SPARTANs are usually enough.**

 **Disclaimer: Boilerplate, boilerplate, I own nothing, blah blah blah, I make no money off this.**

Velasquez sighed as he handed his gear to a tech for repair. That last mission had been a massive clusterfuck. If it hadn't been for the mysterious new arrivals, he doubted that he and Zhang would have survived. Speaking of the unusual soldiers, he noticed that OSIRIS looked a lot more relaxed than Blue Team. The latter were inspecting their gear and it seemed that Kelly, Fred, and Linda were speaking with each other, judging by the way their heads subtly moved. Every once in a while, one of them would shoot a glance at the Master Chief. He walked over to Buck. "Why haven't they taken off their helmets? I mean, this isn't a combat zone, and you guys don't seem to have a problem with it."

"Oh, that?" replied the man, "they're IIs. The armor is pretty much a second skin to them."

"So there are different types of SPARTANs?"

"Yup, the Is were an early supersoldier project. The IIs were the most successful. Chief there is responsible for over 30,000 kills. The IIIs were cheaper to train. In fact, a team of IIIs saved my ass back on Reach." Velasquez noticed Buck's eyes harden at that word. "We IVs aren't as strong or as fast as the IIs, or even the IIIs, but pretty much anyone can become a SPARTAN-IV. For example, I used to be an ODST. There's quite a lot more than that, but we'll save that for whomever's in charge."

"So, who were those 'covies' you referred to back on the skyranger?"

Buck took a deep breath, and in that moment, Velasquez saw an old, tired soldier. "The covenant," he said with bitterness in his voice. "Let's just say that this isn't the first time I've faced down homicidal aliens." His face quickly settled into an emotionless mask. "Well, I guess we'd better talk to the big cheese, so take us to your leader."

 **Now, I know that this is short even by my standards, but I'm nursing a nasty head cold on top of the stomach bug that refuses to die, so I've not been feeling too hot. As an offering, here is a teaser for a story that I will do once this has reached its halfway mark.**

 _Коммунисты были отбиты, и спартанский приказ восстановление после его потери в битве за клад в центре метро-2. Рейх отступили лизать свои раны, и жизнь пошла на, как это было, поскольку мир был казнен. То есть, до тех пор, Хан не появился еще раз, в сопровождении четырех незнакомцев в метро._


	4. Chapter 4

**A/N: Cold's gone, but the stomach bug is more tenacious than I thought. My RWBY/Metro crossover will not be put up at this story's halfway point, as I'm going to do a little more planning for it. Instead, I have another crossover that will be easier for me. A preview will be in the post-script.**

 **XCOM HQ, 2015**

Commander Adrian Whitcombe was intrigued. The footage from Operative Velasquez's helmet-cam showed the eight newcomers tearing a bloody swathe through the aliens that had nearly wiped out Strike One. He stood up, and straightened his tie. Perhaps these strange warriors could be the key to victory. He pressed a button on the intercom device on his desk. "Bradford, are our guests ready for their debriefing?"

"Affirmative, sir."

"Send them in."

"Yes, sir."

The door opened, and the SPARTANs walked in. They all saluted. "At ease, soldiers," Adrian said. After they had dropped into parade rest, he motioned for them to sit down. "Now, that was some damn fine work out there. However, I must know who you are, and how you arrived."

The leader of the smaller group, Locke as he remembered, replied. "We are UNSC SPARTAN-IV supersoldiers. The others are SPARTAN-IIs. Our armor is designated MJOLNIR, with the lighter GEN-2 armor for my team, and the Mk. VII for Blue Team."

"SPARTANs? MJOLNIR? I do not know any of those terms. As for the UNSC, I've never heard of any organization by that name."

"That's what I'm getting to, Commander. We were on the Forerunner Shield World Genesis, rescuing Blue Team, when a security device installed on their prison by Cortana activated. We woke up in Hong Kong."

Whitcombe noticed that one of the SPARTAN-IIs stiffened slightly at the name Cortana. Perhaps it was worth finding out who they were. "What sort of security device?"

"Some kind of Slipspace Portal."

"I don't understand any of this. Perhaps we should start with your history."

"The SPARTAN project began with the ORION Project, originally launched in 2321, then relaunched in 2491."

"So you're from the future."

"No, sir, there are no records of first contact of any sort from this time period. Slipspace is still mostly unknown. Entire ships have vanished, only to reappear without crew. Some never reappear at all."

At that point, Buck added, "Well, I think we now know what sorta happened to them."

"Correct. I believe that we should get back on track. The SPARTAN-Is had enhanced physical and mental attributes, but the program wasn't cost-effective. In 2517, some of the outer colonies started destabilizing. In response, the SPARTAN-II program was greenlit. Most of the details are classified, but the SPARTAN-IIs were a success. Before augmentation, they were already the best humanity had to offer. Afterwards, they became the greatest soldiers in human history. Their counterinsurgency ops in the outer colonies were instrumental to ensuring that the UNSC didn't split apart. However, the insurrection was the least of our worries. In 2525, an orbital platform in orbit around the colony of Harvest made contact with an unknown ship. Contact with Harvest was soon lost. We sent a battlegroup to investigate, and we found the planet glassed. We also found an alien battleship in orbit. We engaged, and were almost wiped out. Only the _Heracles_ managed to escape. The war lasted thirty years, colonies falling one by one. Eventually, only Earth remained. The Covenant then betrayed one of their member species, who then allied with us. Currently, only pockets of Covenant remain."

"You said _colonies_. What were the casualties?"

"Before the war, Humanity numbered in the trillions. After, we were less than half a billion."

Whitcombe froze in shock. "We must never let that happen here. I hereby offer you a place in the XCOM project. We are Humanity's first, last, and _only_ line of defense. With your help, I believe that we can turn the tide of this war. We may finally be able to come out of the shadows, and attack the aliens directly. Will you help us?"

The leader of the SPARTAN-IIs, the Master Chief as he recalled, spoke for the first time. "We accept."

 **Another short chapter. Sorry about that. (It takes a bit to work everything out.) Anyway, as promised, here is the preview!**

Ruby and Weiss walked through the Emerald Forest. "Ruby, admit it, _you_ got us lost."

"Not lost, just an... unplanned detour!"

Weiss sighed. Her partner obviously didn't understand the gravity of the situation. Why, the team they were assigned to would reflect on them as well. It was bad enough that she was partnered with this child, but if she was put on a team with, Oum forbid, said child's sister, she didn't know how she would stay sane. She paused upon hearing a loud roaring like ten thousand Grimm. Terror shot through her. They were obviously going to be swarmed and devoured. That train of thought was cut off as she was hit with a body that fell from above. She groaned, then groaned again as three more landed on top of her. "RUBY!" she called, and her partner arrived to pull her out. They stared at the pile of unconscious bodies. At the bottom was a figure in heavy plate armor, with a massive shield in his left hand. Lying on top of him was another figure, this one in a brown longcoat with the collar turned up and spiked metal shoulders and gauntlets, giving him a sinister appearance. Lying on top of him was a young woman in light armor with purple robes underneath. On top of _her_ , however, was the most interesting. He wore formfitting leather armor with countless pockets and strange vials attached. A leather hood obscured the top half of his face, the shadows clinging to it unnaturally. Around his neck was wrapped a red scarf, worn and tattered. Ruby moved to touch it, and the stranger groaned. Underneath the hood, two eyes that glowed a baleful yellow opened.

 **Stay tuned for** _ **And The Heavens Shall Tremble**_ **!**


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